In a printer that uses a transfer film ribbon (hereinafter referred to as ribbon) such as a thermal transfer film, the ribbon and a paper sheet are delivered in pressure contact between a head and a platen. If the ribbon tension varies as this is done, the feed of the ribbon is not concurrent with the feed of the paper sheet. Therefore, the ribbon may wrinkle or rub against the paper sheet, so that the print quality may be ruined in some cases.
In order to reduce the variation of the ribbon tension, in a conventional printer such as the one described in Japanese Patent Application Laid-Open No. 62-113581, a motor for a ribbon feed shaft is driven to accelerate ribbon feed if the tension of that part of the ribbon on the upstream side of the platen becomes too high. If the tension of that part of the ribbon on the downstream side of the platen becomes too low, on the other hand, a motor for a ribbon take-up shaft is driven to accelerate ribbon winding. Thus, the tension is standardized in both those parts of the ribbon on the upstream and downstream sides of the platen.
In the example described above, the ribbon tension is detected by rocking a tension arm that has a ribbon retainer portion on its distal end. This tension arm has one end rockably mounted on a printer frame and is urged in one direction by a spring. The ribbon retainer portion on the distal end has a function to remove looseness from the ribbon by engaging the ribbon.
However, the length of the tension arm must be extended in order to remove the looseness of the ribbon effectively by means of the tension arm. In consequence, an installation space must be secured lest the long tension arm interfere with other elements that constitute the printer even when it is rocked.
Further, the ribbon retainer portion that is mounted on the distal end of the tension arm has no function to remove wrinkles from the ink ribbon, although it engages the ribbon.